H-20 is one of the four standard load classes developed by the American Association of State Highway and Transportation Officials (AASHTO...earlier AASHO)for highway and bridge design. It designates both the max. load and load distibution among axles, i.e. for a 20-ton truck "H-class" truck (who knows how they decided on these designations for trucks!)with two axles (front single wheels, rear dual wheels) the distribution is 8000 lbs. for the front axle and 32,000 lbs. for the rear axle.<br><br>This system is somewhat confusing when trying to apply this nomenclature to present vehicle configurations and loads (the AASHTO designations date back to 1935 and 1944). I typically design pavement structures using the maximum allowable total weight of a 5-axle semi-tractor/trailer having 2 tandem axles and 1 single axle with a distribution of 18k on each of the rear axles, 16k on each of the two rear tractor axles and 12k on the front single axle, for a total of 80k. This is a typical weight limit for many states. Individual axle loads are usually limited to 20 or 22k.<br><br>For bridge design, consult the AASHTO Standard Specifications for Highway Bridges to get the load configuration for rolling load considerations. For pavement section design with either rigid or flexible pavement, you can use something similar to what I described.
In order to determine the concrete thickness, would need to know several pieces of info....<br><br>Need to know subbase type and strength<br>Need to know expected joint pattern and joint type for pavement<br>Need to know traffic...character and frequency<br>Need to know local capability to produce consistent concrete and type of coarse aggregates available locally<br><br>Without this info,not practicable to give definitive answer. For "ballpark", you should be in the 6 to 8 inch thickness range.
